[英]Why am I getting a NullPointerException on this line?
我以前運行良好的代碼現在正在拋出NPE。 它也不是換行的,所以我很困惑。 有人可以指出我正確的方向嗎?
確定問題線的位置大約在一半以下。
public class FavouritesActivity extends Activity {
private String mFavourites;
ArrayAdapter <String> adapter;
List<String> list;
private ListView lv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_favourites);
lv = (ListView) findViewById(R.id.My_Favourites);
SharedPreferences preferences = this.getSharedPreferences("MyPreferences", Context.MODE_PRIVATE);
list = new ArrayList<String>();
Map<String, ?> prefsMap = preferences.getAll();
for (Map.Entry<String, ?> entry: prefsMap.entrySet()) {
list.add(entry.getValue().toString()); //THIS IS THE PROBLEM <<<<<<<<<<<<<<<<<<
}
adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, list);
lv.setAdapter(adapter);
lv.setOnItemLongClickListener(new OnItemLongClickListener() {
// setting onItemLongClickListener and passing the position to the function
@Override
public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
int position, long arg3) {
String mFavourites =(lv.getItemAtPosition(position).toString());
removeItemFromList(position);
return true;
}
});
}
protected void removeItemFromList(int position) {
final int deletePosition = position;
AlertDialog.Builder alert = new AlertDialog.Builder(
FavouritesActivity.this);
alert.setTitle("Delete");
alert.setMessage("Do you want delete this item?");
alert.setPositiveButton("YES", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// TOD O Auto-generated method stub
// main code on after clicking yes
list.remove(deletePosition);
Operator();
adapter.notifyDataSetChanged();
adapter.notifyDataSetInvalidated();
}
});
alert.setNegativeButton("CANCEL", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
dialog.dismiss();
}
});
alert.show();
}
protected void Operator() {
SharedPreferences preferences = this.getSharedPreferences("MyPreferences", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.remove(mFavourites);
editor.commit();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.my_supplements, menu);
return true;
}
}
這是LogCat:
01-10 14:08:59.850: E/AndroidRuntime(2194): FATAL EXCEPTION: main
01-10 14:08:59.850: E/AndroidRuntime(2194): Process: com.LifeSchematics.msg, PID: 2194
01-10 14:08:59.850: E/AndroidRuntime(2194): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.LifeSchematics.msg/com.LifeSchematics.msg.FavouritesActivity}: java.lang.NullPointerException
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.app.ActivityThread.access$800(ActivityThread.java:135)
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.os.Handler.dispatchMessage(Handler.java:102)
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.os.Looper.loop(Looper.java:136)
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.app.ActivityThread.main(ActivityThread.java:5017)
01-10 14:08:59.850: E/AndroidRuntime(2194): at java.lang.reflect.Method.invokeNative(Native Method)
01-10 14:08:59.850: E/AndroidRuntime(2194): at java.lang.reflect.Method.invoke(Method.java:515)
01-10 14:08:59.850: E/AndroidRuntime(2194): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
01-10 14:08:59.850: E/AndroidRuntime(2194): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
01-10 14:08:59.850: E/AndroidRuntime(2194): at dalvik.system.NativeStart.main(Native Method)
01-10 14:08:59.850: E/AndroidRuntime(2194): Caused by: java.lang.NullPointerException
01-10 14:08:59.850: E/AndroidRuntime(2194): at com.LifeSchematics.msg.FavouritesActivity.onCreate(MySupplementsActivity.java:40)
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.app.Activity.performCreate(Activity.java:5231)
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-10 14:08:59.850: E/AndroidRuntime(2194): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
之所以得到NullPointerException,是因為某些首選項值存儲為null,而entry.getValue()為null。 因此,在調用toString()之前添加null檢查
for (Map.Entry<String, ?> entry: prefsMap.entrySet()) {
final Object value = entry.getValue();
list.add(value == null ? "null" : value.toString());
}
要么
for (Map.Entry<String, ?> entry: prefsMap.entrySet()) {
final Object value = entry.getValue();
if (value != null) {
list.add(value.toString());
}
}
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